See WIKI here for modeling a trunnion attachment in AutoPIPE. As mentioned a trunnon modeled with Beam elements will not appear on a stress iso. This has been logged as a new enhancement (1042361).
Stress ISOmetric, I would like to see the trunnions shown along with their attached supports
This will definitely save time having to annotate stress isos to show the misssing pipe supports with the trunnions.